This application claims the benefit of Belgian Application No. 2001/0200 filed Mar. 27, 2001.
The invention relates to a device for adjusting the tension in pile warp yarns in a face-to-face weaving machine, the device comprising a first and a second yarn guiding element, the second yarn guiding element adjusting the tension in the yarn by deflection.
A similar device is already known in face-to-face weaving machines, in which a device is provided between each pile warp yarn beam and the pile supplying cylinder in order to stretch the pile warp yarns. The device consisting here of a cylinder which is rotatable around a hinge shaft to which a second cylinder, rotatable round a hinge shaft, is connected by means of a lever system. The deflection of this second cylinder causes the pile warp yarns to be stretched. This deflection is obtained by tightening a spring, more particularly draw-springs and torsion springs.
The problem of this device is, that because of the known spring rate, with each position of the deflection of the dancer cylinder another tension is built up in the pile warp yarns. The real tension is situated, as it were, with a hysteresis loop around an average value. In weaving machines running at higher speeds, at a start, the pile length is taken up faster per time unit by the pile suppliers and at a stop the decrease of pile warp yarns per time unit is also stopped quicker, so that shocks will occur in the spring system, causing oscillations of the stretching device. Moreover, at each replacement of a pile warp yarn beam the pre-load of the spring system is released, after which, after having tied Up the new pile warp yarn beam, the pre-load of the spring system must be readjusted. This adjustment is done manually and requires the survey or measuring of the elongation or the torsion of the spring, because of which the operations required by this device are time-consuming
The purpose of this invention is a device for adjusting the tension in pile warp yarns in a device which does not show any of the drawbacks mentioned above.
According to the invention, this purpose is obtained in providing a pneumatic system in which the pressure in the pneumatic system determines the deflection of the second yarn guiding element and in which the pneumatic system is provided to keep the pressure at a practically constant value, adjusted via the control system.
This has the advantage that the hysteresis loop which shows the real tension in the device according to the state of the art, will be reduced and will approach as much as possible the average value adjusted via the control system.
In a preferred embodiment the tension in the pile warp yarns is adjustable by adjusting a certain pressure in the pneumatic system.
On the one hand, this has the advantage that for a well-specified application a well-specified pressure may be adjusted via the control system of the face-to-face weaving machine, which varies, for instance, when using a different type of yarn.
On the other hand this has also the advantage that the tension in the pile warp yarns may be released or reduced for certain operations which have to be carried out on the face-to-face weaving machine, for instance, when changing the pile warp yarn beam.
In a preferred embodiment of the device the pressure in the pneumatic system can be adjusted by means of a valve.
In a more specific preferred embodiment of the device, the valve can be controlled by the control system of the face-to-face weaving machine.
This has the advantage that the tension in the pile warp yarn can be adjusted with a numerical value for the working pressure via the keyboard of the control system of the face-to-face weaving machine.
In a particularly advantageous embodiment of the device, the pneumatic system determines the deflection of the second yarn guiding element via a lever system that is situated between the first and second yarn guiding element.
This has the advantage that the working pressure in the pneumatic system can be maintained at a constant value by means of a regulating valve, regardless of the position of the second guiding element.
In a particularly preferred embodiment of the device, the pressure adjusted in the pneumatic system is readable on the control panel of the face-to-face weaving machine.
This has the advantage that for a certain type of yarn and type of fabric the working pressure can be read exactly and stored in a file containing the adjusting parameters of the face-to-face weaving machine for that type of fabric.
In a more specific preferred embodiment of the device, the pneumatic system works based on compressed air.
This has the advantage that a certain pressure in the delivery pipe can be easily increased to a certain working pressure by means of a regulating valve.
It is an understood thing that these advantages cannot only be obtained in face-to-face weaving machines, but also in other textile machines, for applications with other yarns.
This invention is further clarified in the following non-restrictive description of a preferred embodiment of a pile warp yarn stretching device according to this invention.